1. Field of the Invention
The present invention relates to a hardness tester and a hardness test method.
2. Description of the Related Art
Conventionally, there is a press-type hardness test method which measures hardness of a sample by pressing an indenter in the shape of a polygonal pyramid onto the surface of the sample, and measuring the lengths of the diagonal lines of a polygonal indentation formed on the surface of the sample. As such a hardness test method, the Vickers hardness test method, the Knoop hardness test method, and the like are well known. The method is often used to evaluate mechanical properties of metallic materials.
As it is well known, the Vickers hardness test method uses an indenter in the shape of a square (or rhombic) pyramid made of diamond, and shows the hardness of a sample from the perspective of a relationship between the average value of the lengths of the two diagonal lines of an indentation in the shape of a square pyramid formed on the surface of the sample and a force (a load) pressed onto the sample by the indenter. The Knoop hardness test method uses an indenter in the shape of a rhombic pyramid (an extended pyramid) made of diamond, and shows the hardness of a sample from the perspective of a relationship between the length of a longer diagonal line of the two diagonal lines of an indentation in the shape of a rhombic pyramid formed on the surface of the sample and a force (a load) pressed onto the sample by the indenter.
Incidentally, a hardness test and tissue observation of a metallic material are often carried out together. In general, in a well-known hardness tester, when a hardness test of a metallic material is carried out, binarization processing is performed on a picked-up image of the surface of a sample picked up by an image pickup section on the basis of determination whether or not a brightness value is less than a predetermined value, so as to extract an indentation region formed on the surface of the sample, which is disclosed by Japanese Patent No. 4029832, for example. However, when a hardness test is carried out after etching processing is performed on the surface of a sample for tissue observation, brightness distribution of a picked-up image of the surface of the sample is complicated, and accordingly, it is hard to recognize an indentation formed on the surface of the sample. As a result, an indentation region cannot be extracted correctly.
Then, in order to solve the abovementioned problem, a technology is disclosed by Japanese Patent No. 3557765, for example. By the technology, images of the surface of a sample are picked up before and after an indentation is formed thereon, and an indentation region is extracted based on a difference between the picked-up image which is picked up before the indentation is formed and the picked-up image which is picked up after the indentation is formed.